Down Syndrome (DS) children have particular difficulty perceiving and producing speech. Previous research has suggested that rate-dependent speech processing may be different in DS individuals. Such differences would have profound implicatins for speech processing in general since the ability to adjust or "normalize" across differences in speaking rate is fundamental to mature speech perception. The development of the ability to normalize temporal perception for varying rate contexts has not been considered in previous research with either normally developing or DS infants and children. The present proposal seeks to fill this gap by addressing the effects of temporal variation on the perception of segment duration within the context of the developing perceptual systems of infants and young children. The research will address infant, child and adult abilities to discriminate context-dependent duration cues involving four different segment types: steady-state vowels, stop consonant silences, transitions from consonants to vowels and consonantal noise or frication. Using the VRISD (Visually Reinforced Infant Speech Discrimination) paradigm, as well as age-adapted versions of this paradigm, the discrimination and categorization of durations of both speech and non-speech stimuli will be studied. Results should provide a framework for understanding the development of the capacity to normalize speech rate in a variety of important speech contexts in both DS and normally developing infants. By contrasting the results for speech and non-speech stimuli, the influence of general perceptual tendencies and of specific speech processing strategies can be specified as well.